1. Field of the Invention
The present invention relates to a mobile telecommunication of third generation, and more particularly to a method for transmitting a transport format combination indicator (TFCI) inserted to each time slot of a radio frame in a mobile telecommunication system using a W-CDMA standard.
2. Discussion of the Related Art
Generally, a Third Generation Partnership Project (3GPP) group describes a definition of a physical channel of an upward link and a downward link of Radio Access Network (RAN). Here, a Dedicated Physical Channel (DPCH) comprises three-layer structure of super frames, radio frames and time slots. FIGS. 1 and 2 show two data structures of the DPCH. The first type is a Dedicated Physical Data Channel (DPDCH) for transferring dedicated data, and the second type is a Dedicated Control Channel (DPCCH) for transferring a control information.
FIG. 1 shows a data structure of an upward link DPCH according to the standard of 3GPP RAN, while FIG. 2 shows a data structure of a downward link DPCH. In FIGS. 1 and 2, the DPCCH includes a TFCI field in each time slot constituting a radio frame. In other words, information on a transmission format, i.e. TFCI, is coded and inserted into each radio frame.
The coding of the TFCI bits according to the 3GPP standard will next be explained.
The number of TFCI bits is variable from a minimum of 1 bit to a maximum of 10 bits, and the number of bits is determined from the point in time when a call starts through a signal processing of an upper layer, Different coding methods are applicable to the TFCI depending upon the number of bits. When the number of TFCI bits is less than 6, a bi-orthogonal coding or a first Reed-Muller coding is applicable. When the number of the TFCI bits is greater than 7, a second Reed-Muller coding is applicable. According to the 3GPP standard, the coded TFCI undergoes a puncturing to generate a code word of 30 bit length.
For example, when the number of TFCI bits, determined by upper layer signaling, is less than 6, a TFCI code word is output through a bi-orthogonal coding. Here, a (32, 6) coding is applicable to the bi-orthogonal coding. For that purpose, if the TFCI consists of less than 6 bits, a padding procedure is first executed to supplement the deficient bit value with xe2x80x9c0xe2x80x9d from the Most Significant Bit (MSB). Thereafter, the TFCI code word is inserted into each time slot of a radio frame by two bits. However, the entire length is restricted to be 30 bits. Thus, the TFCI code word of 32 bits, which has been bi-orthogonal coded, is punctured by 2 bits and inserted into each time slot.
In another example, when the number of TFCI bits determined by upper layer signaling not more than 10 bits, a TFCI code word is output through a second Reed-Muller coding. Here, a (32, 10) coding is applicable to the second Reed-Muller coding. For that purpose, if the TFCI bits are less than 10, a padding procedure is first executed to supplement the deficient bits with xe2x80x9c0xe2x80x9d from the MSB. The Reed-Muller coded TFCI code word is referred to as a sub-code, Accordingly, the sub-code is punctured by 2 bits to also generate a TFCI code word of 30 bit length. FIG. 3 is a block diagram illustrating a channel coding process.
The code word of 30bit length generated as described above is divided into fifteen 2-bits and inserted into each time slot for transfer. FIG. 4 is a diagram showing a typical insertion of the coded TFCI code word into each time slot.
Also, FIG. 5 is a diagram illustrating an encoding structure for generating a (32, 10) TFCI code word according to the conventional second Reed-Muller coding. Referring to FIG. 5, the TFCI bits, variable from 1 to 10 bits are input to an encoder. The input data bit is lineally combined with 10 basis sequences. Namely, the basis sequences (32 element vectors) used for the linear combination comprises of a uniform code, in which all bit values are xe2x80x9c1xe2x80x9d; five orthogonal variable spreading factor codes represented by {C32, 1, C32, 2, C32, 4, C32, 8, C32, 16} as shown in Table 1; and four mask codes represented by {Mask1, Mask2, Mask3, Mask4} as shown in Table 2. In the conventional second Reed-Muller coding, the four mask codes are used to increase the number of code word by 16 times.
Table 3 below shows the prior basis sequences, in which Mi,0 is the uniform code; Mi,1xcx9cMi,5 respectively corresponds to C32,1, C32,2, C32,4, C32,8, and C32,16; and Mi,6xcx9cMi,9 respectively corresponds to Mask1xcx9cMask4.
The TFCI bits are lineally combined with the basis sequences described above and can be expressed by Equation 1, in which a0 represents the Least Significant Bit (LSB), while anxe2x88x921 represents the MSB.
anxe2x88x921, anxe2x88x922, . . . , a1, a0(nxe2x89xa610)xe2x80x83xe2x80x83[Equation 1]
A TFCI code word of 30 bit length is subsequently output by puncturing the first and the 17th bits from the (32, 10) sub-code generated by the linear combination.
The output TFCI code word of 30 bit length can be expressed by Equation 2:
b0, b1, b2, . . . , i28, b29xe2x80x83xe2x80x83[Equation 2]
Namely, the TFCI bits are input as expressed by Equation 1 are encoded by Equation 3 below to output the TFCI code word as expressed by Equation 2:
bi=xcexa3(aaxc3x97Mi,n)mod2(from n=0 to n=9, where i=0, 2, . . . , 31)xe2x80x83xe2x80x83[Equation 3]
However, the TFCI encoding according to the technology in the related art as described above poses the following problems. First, the pattern of the TFCI bits input for encoding are improper because of the padding procedure necessary when the TFCI bits are input for coding. Particularly, when the TFCI bits for coding is less than 10, a padding procedure is typically executed to supplement the deficient bit values with xe2x80x9c0xe2x80x9d from the MSB. Therefore, a complex decoding procedure is necessary to decode: the encoded and transmitted TFCI code words at a receiving party. Namely, a bi-orthogonal coding is necessary even when the input TFCI bits is less than 6. Thus, the receiving party needs to perform a priority check to confirm from which set the OVSF code, used for the encoding, has been selected between two OVSF code sets which are in binary complement relations. As a result, additional process and hardware are required.
Also, when two bits are punctured to generate a (30, 10) TFCI code word, inserted and transmitted to the actual TFCI field from the (32, 10) code word, a minimum hamming distance loss is up to 2 at maximum. Furthermore, although not explained above, one bit is punctured in a (16, 5) code word to generate a (15, 5) TFCI code word, In such case, a minimum hamming distance loss also occurs.
Accordingly, an object of the present invention is to solve at least the problems and disadvantages of the related art.
Particularly, an object of the present invention is to allow an easy decoding of TFCI in a mobile telecommunication system of the third generation under a W-CDMA standard.
Another object of the present invention to provide an optimal matrix for basis sequences for TFCI coding.
A still another object of the present invention to provide a method for encoding the TFCI with an optimal matrix for basis sequences.
A further object of the present invention to provide an optimal matrix for basis sequences for TFCI coding which can maximize a minimum hamming distance with respect to a TFCI code word when inserting one or two bits into each time slot and transmitting after puncturing the TFCI code word used in the mobile telecommunication system under the W-CDMA standard.
A still further object of the present invention to provide a method for encoding the TFCI with an optimal matrix for basis sequences which can maximize a minimum hamming distance with respect to a TFCI code word when inserting one or two bits into each time slot and transmitting after puncturing the TFCI code word used in the mobile telecommunication system under the W-CDMA standard.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims.
To achieve the objects and in accordance with the purposes of the invention, as embodied and broadly described herein, two optimal basis sequences for TFCI code are disclosed.
If the TFCI is not more than 10 bits, it is padded with zeros to 10 bits by setting the most significant bits to zero if the bits are less than 10. The resultant 10 bit TFCI is encoded by the (32, 10) sub-code of second order Reed-Muller code. The transmitted code words are linearly combined with 10 basis sequences: {M0, M1, . . . , M9}. The basis sequences are linearly combined with TFCI bits as M0 to the least significant bit and M9 to the most significant bit.
One of the basis sequences of the present invention is as follows: {M0=(All 1""s), M1=C32,16, M2=C32,8, M3=C32,4, M4=C32,2, M5C32,1, M6=Mask1, M7=Mask2, M8=Mask3, M9=Mask4}. With this basis sequence, the TFCI coding scheme for Wide-band Code Divisional Multiple Access Frequency Division Duplex (W-CDMA FDD) standard achieve more diversity gain in fading channel, which results in 0.5-2.5 dB gain in case of 2-5 bits length TFCI.
An alternate basis sequences of the present invention is as follows: {M0=C32,16, M1=C32,8, M2=C32,4, M3=C32,2, M4=C32,1, M5=(All 1""s), M6=Mask1, M7=Mask2, M8=Mask3, M9=Mask4}. With is basis sequence, the TFCI coding, scheme for FDD standard achieves almost the same diversity gain as that of the former.
Since the basis of OVSF codes C32,1, C32,2, C32,4, C32,8, C32,16 correspond to that of Hadamard codes H5,16, H5,8, H5,4, H5,2, H5,1 of length 25=32, optimizing the input pattern is equivalent to exchanging the basis codes from (M0=all 1 s, M1=C32,1, M2=C32,2, M3=C32,4, M4=C32,8, M5=C32,1, M6, M7, M8, M9) to (M0=H5,1=C32,16, M1=H5,2=C32,8, M2=H5,4=C32,4, M3=H5,8=C32,2, M4=H5,16=C32,1, M5=all 1 s, M6, M7, M8, M9).
Therefore, a method according to the present invention for encoding the TFCI comprises determining the number of TFCI bits; Repeating a0 32 times for coding, if the TFCI consist of 1 bit; and linearly mapping t TFCI information bits a0, a1, a2, a3, a4, a5, a6, a7, a8, a9 (a0 is LSB and a9 is MSB) to the basis sequences, if the TFCI consist of more than 2 bits.
A method according to th present invention for encoding TFCI in split mode comprises determining the number of TFCI bits; Repeating a0 16 times for coding if the TFCI consist of 1 bit; and linearly mapping the TFCI information bits a0, a1, a2, a3, a4 (a0 is LSB and a4 is MSB) to the basis sequences, if the TFCI consist of more than 2 bits.